The disclosure relates generally to a spectroscopy system and more specifically to an automatically aligning spectroscopy system adapted for use in vibration prone environments, such as heat recovery steam generator (HRSG) chambers.
Many power requirements benefit from power generation plants that provide low cost energy with minimum environmental impact. In addition, the power generation plants provide better reliability and off-grid operation with alternate fuels such as biogas or landfill gas, with examples being gas turbines and combustion engines. The gas turbines are giant engines, which convert energy of hot pressurized combustion gases into mechanical energy by rotation of a turbine in the engines. Subsequently, this rotation of the turbine is utilized to generate electricity by using a generator. Thereafter, in a combined cycle plant, the exhaust or residual gases from the gas turbines are let out into the atmosphere through the HRSG chamber and a stack. These exhaust gases include traces of environment unfriendly gases that can be potentially hazardous to the atmosphere and human health. Therefore, it is of great interest and concern to identify the constituents and concentration of the exhaust gases and minimize the emission of unfriendly gases to the environment.
Currently, extractive techniques are available for monitoring the constituents and concentration of the exhaust gases, especially a target gas in the exhaust gases. The main idea of these techniques is that a sample of the exhaust gases is extracted and conveyed to analyzers through sample lines. Further, the constituents and concentration of the target gas is measured by offline measurement techniques, such as infrared and/or ultraviolet absorption measurements. Unfortunately there is a significant delay between the time of gas extraction and the analysis that follows to measure the constituents and concentration of the target gas. Thus, these techniques fail to facilitate a better control on emission of exhaust gases to the environment.
The alternative technique that can be employed to address this problem is Tunable Diode Laser Absorption Spectroscopy (TDLAS). TDLAS is typically implemented with diode lasers operating in the near-infrared and mid-infrared spectral regions. Various techniques of TDLAS for sensing and control of combustion processes have been developed. Commonly known techniques are wavelength modulation spectroscopy, frequency modulation spectroscopy, and direct absorption spectroscopy. Each of these techniques is based upon a determined relationship between the quantity and nature of laser beam received by a detector after the laser beam passes through an absorption media, such as gases inside the HRSG chamber. The laser beam, in specific spectral bands, may be absorbed by gas species in the chamber. The absorption spectrum of the laser beam received by the detector is used to determine the constituents and/or concentration of the gas species.
In these techniques, TDLAS is typically mounted in the stack to determine the constituents and/or concentration of the exhaust gases inside the chamber. The stack may be a small cylindrical pipe disposed at an outlet side of the HRSG chamber for releasing the residual gases to the atmosphere. However, the TDLAS may also be implemented in the HRSG chamber for desirable applications such as gas concentration measurement, gas temperature measurement, gas pressure measurement etc. Unfortunately, implementing the TDLAS in the HRSG chamber is difficult due to harsh conditions, vibrations, and thermal variations in the HRSG chamber. These conditions may cause misalignments of the TDLAS system leading to erroneous measurements of the exhaust gases.
Currently, there are various techniques to rectify the misalignment of TDLAS system. One way of correcting the misalignment of TDLAS system is to manually rectify or adjust the misalignment of the TDLAS system. However, manually adjusting the TDLAS system is a time consuming process as an operator may have to reach for the TDLAS system to manually adjust the TDLAS system. Also, manually adjusting the TDLAS system may be impractical in an operational power plant. Further, since the operator is unaware of a direction of misalignment of the TDLAS system, the operator may have to employ a trial and error method, which is again an inefficient and time consuming process.
It is therefore desirable to develop a design of a TDLAS system that reduces such erroneous measurements. Particularly, it is desirable to develop the design of the system that detects the misalignment in the TDLAS system and automatically aligns the TDLAS system, irrespective of the environmental conditions in and around the HRSG chamber.